NO WAY would I stay there. Snakes are common here in older farm homes, and the favorite guests are black snakes that reach 6-8 feet long! My friend was renting a 2-story farm home, and she found one (5 ft) in her bathroom.
They are harmless, and I am not afraid of snakes since we don't have venomous ones here, but still I will not share my home with a free roaming snake! Even worse for your SIL because it could be venomous living in TN. I sure hope she finds it. To get rid of the snake or future snakes, you must get rid of their food source. If they are in your home, there is a good chance there are mice close by.